EP3627093B1 - Vorrichtung zur parallelen optischen kohärenztomographie-bildgebung im fourier-bereich und bildgebungsverfahren mit verwendung von paralleler optischer kohärenztomographie im fourier-bereich - Google Patents

Vorrichtung zur parallelen optischen kohärenztomographie-bildgebung im fourier-bereich und bildgebungsverfahren mit verwendung von paralleler optischer kohärenztomographie im fourier-bereich Download PDF

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EP3627093B1
EP3627093B1 EP18461611.8A EP18461611A EP3627093B1 EP 3627093 B1 EP3627093 B1 EP 3627093B1 EP 18461611 A EP18461611 A EP 18461611A EP 3627093 B1 EP3627093 B1 EP 3627093B1
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light
imaging
optical
phase
det
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EP3627093A1 (de
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Patrycjusz STREMPLEWSKI
Maciej Wojtkowski
Pawel Wnuk
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Instytut Chemii Fizycznej of PAN
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02041—Interferometers characterised by particular imaging or detection techniques
    • G01B9/02044—Imaging in the frequency domain, e.g. by using a spectrometer
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/102—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for optical coherence tomography [OCT]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
    • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
    • G01B9/02004—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using frequency scans
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
    • G01B9/0201—Interferometers characterised by controlling or generating intrinsic radiation properties using temporal phase variation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02034—Interferometers characterised by particularly shaped beams or wavefronts
    • G01B9/02038—Shaping the wavefront, e.g. generating a spherical wavefront
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02062—Active error reduction, i.e. varying with time
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02075—Reduction or prevention of errors; Testing; Calibration of particular errors
    • G01B9/02082—Caused by speckles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02083—Interferometers characterised by particular signal processing and presentation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/0209—Low-coherence interferometers
    • G01B9/02091—Tomographic interferometers, e.g. based on optical coherence
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/65—Spatial scanning object beam

Definitions

  • the invention relates to an apparatus for Optical Coherence Tomography imaging with parallel Fourier domain detection and a method of imaging by Optical Coherence Tomography with parallel Fourier domain detection, which can be used for in-vivo imaging, in particular for imaging of the retina and anterior chamber of the eye, but also for imaging of other organs, tissues and cells.
  • the invention enables the reconstruction of the three-dimensional structure of objects without disturbances resulting from phase modulation of scattered light.
  • OCT Optical Coherence Tomography
  • a device that consists of a light source emitting light of multiple wavelengths which, after collimation, passes to an interferometer consisting of a beam splitter, a reference mirror, an optical system forming light on the object in the interferometer's sample arm and an optical system forming light on the reference mirror in the interferometer's reference arm.
  • OCT Optical Coherence Tomography
  • the method of imaging objects by means of this system is based on the interference of the beam of light reflected from the reference mirror with the beam of light scattered on the structural components of imaged object.
  • the electrical signals obtained by the detector are processed by a computer.
  • Parallel detection means that a multi-element photodetector is used and in a single exposure of the detector, linear or two-dimensional Optical Coherence Tomography data are recorded.
  • Such detector can be a one or two-dimensional array of photosensitive components (for example a CMOS camera, CCD, linear CCD camera).
  • the collection of this sort of data allows for the 3D reconstruction of the object (in the case of an array and a tunable laser source) or image cross-section (in the case of a line of detectors and a tunable laser source or an imaging spectrometer and a temporally incoherent light source).
  • the Z axis coincides with the direction of light beam propagation (into the depth of the object) and the X and Y axes correspond to directions perpendicular to the direction of propagation of the beam illuminating the object (they symbolize directions on the surface of the object).
  • a complex representation of spectral interference fringes in which there is information about the phase of the interference fringes, is used.
  • a complex representation is obtained after adding the original signal of spectral interference fringes (as the real part) to its Hilbert transform (as the imaginary part).
  • the complex signal representation can also be obtained by measuring at least three spectral interference fringe signals by phase shifting methods ( Schwider, J. et al. Digital wave-front measuring interferometry: some systematic error sources. 22, 3421 (1983 ).)
  • Complex representations of interferometric signals can be averaged in a complex manner by adding the real and imaginary parts separately and repeat presentation of the resultant signal as a complex number.
  • the shape of the interference fringes is the result of combining multiple optical fields that contain time-constant phase relations (stationarity of optical processes).
  • Most of the known light detectors such as CCD cameras or CMOS cameras integrate signals during the exposure time of the camera, averaging many optical fields. This averaging process, taking place while the camera is recording and averaging the representation of complex signals, considers the phase relations of the interference fringes in the same manner, giving the same final result. Therefore, in the further part of the description, averaging of the spectra obtained directly from the measurement (by integrating signals on the camera during the recording process), shall also be referred to as complex averaging.
  • Known OCT systems with parallel detection and those operating on the basis of Fourier domain detection use spatially coherent radiation sources.
  • Spatially incoherent sources are used in systems with parallel detection in the time domain, which are inherently less sensitive than systems with Fourier domain detection.
  • OCT optical coherence tomography
  • the natural optical system of the eye is usually used as the component of the system forming light on the object, which is the retina of the eye.
  • OCT techniques enable the visualization of retinal cross-sections in a non-invasive and noncontact way.
  • the disadvantage of these methods and, in particular, methods with parallel Fourier domain detection is, however, the inability to visualize the deeper layers such as the choroid, which are located under the Retinal Pigment Epithelium (RPE) which strongly scatters light, preventing the tomographic reconstruction of the layers underneath.
  • RPE Retinal Pigment Epithelium
  • Fig. 2 The problem of visualizing the deeper layers of the object, in the case of using spatially coherent sources in the system with parallel detection, is associated with the presence of a phenomenon called optical crosstalk, which limits the capabilities of imaging in objects that scatter light such as the choroid or skin.
  • the creation of the crosstalk is illustrated in Fig. 2 , where continuous and dashed lines are used to distinguish between the radiation from two areas of light source, which after passing through the beam splitter BS reach the object Ob, after reflection or scattering from the object they reach the optical system forming an image of the object on the camera array DET.
  • each of the distinguished rays contributes to the signal in only one allocated area of the detector, which does not coincide with an area assigned to any other rays ( Fig. 2a ).
  • an interferometer in the system for the optical selection of the imaging plane that is applied to samples of considerable thickness, an interferometer is used and the sample is illuminated by a random light field.
  • illumination is achieved by means of a rotating diffuser placed in front of the interferometer and a laser with high temporal coherence ( Choi, Y., Yang, TD, Lee, KJ & Choi, W. Full-field and single-shot quantitative phase microscopy using dynamic speckle illumination, Opt. Lett.36, 2465, 2011 ) or light sources with a wide emission spectrum ( Choi Y. et al, Dynamic speckle illumination wide-field reflection phase microscopy. Opt. Lett.
  • the visualization of the deeper layers of the object when using OCT with parallel Fourier domain detection, as with other OCT techniques, is affected by speckle noise that makes it difficult to distinguish details of images at the nominal resolution level of these systems, since the dimensions of the speckles are usually greater than or comparable to the resolution of OCT methods. This applies to both the image dimension in the plane perpendicular to the direction of light propagation (XY direction) as well as in the direction parallel to the direction of light propagation (Z direction).
  • the mechanism of speckle formation is slightly different in these two dimensions and it is associated with the property of light coherence.
  • the speckle image in the XY plane is dependent on the numerical aperture of the imaging system, whereas the speckle pattern in the Z direction depends on the central wavelength and the spectral width of the light source.
  • the first is the aforementioned optical crosstalk
  • the second mechanism is related to the limited spatial resolution of the imaging system. This second mechanism is also important in other types of OCT systems, which use the scanning of a beam focused on the object, e.g. in Spectral domain OCT or Swept Source OCT techniques.
  • Within the distinguishable volume component both optically in the X, Y plane, and temporally in the Z axis) there are many scattering centres.
  • the total field scattered in such a volume component into a solid angle corresponding to the numerical aperture of the detector is the coherent superposition of the waves coming from the optically indistinguishable scattering centres within this volume.
  • This coherent superposition means that a given volume component can be seen in the OCT reconstruction as a light or dark area.
  • Methods and devices are disclosed in using a wavefront corrector to compensate for the aberration information provided by CG-WFS in a combined imaging system, that can use one or more channels from the class of (i) optical coherence tomography, (ii) scanning laser ophthalmoscopy, (iii) microscopy, such as confocal or phase microscopy, (iv) multiphoton microscopy, such as harmonic generation and multiphoton absorption.
  • a swept source that drives both an OCT channel and a coherence gated wavefront sensor, where: a) both channels operate according to SS-OCT principles; b) OCT channel integrates over at least one tuning scan of the swept source to provide a TD-OCT image of the object; c) CG-WFS integrates over at least one tuning scan of the swept source to provide an en-face TD-OCT mapping of the wavefront.
  • simultaneous and dynamic aberration measurements/correction with the imaging process is achieved.
  • the methods and devices for depth resolved aberrations disclosed will find applications in wavefront sensing and adaptive optics imaging systems that are more tolerant to stray reflections from optical interfaces, such as reflections from the microscope objectives and cover slip in microscopy and when imaging the eye, the reflection from the cornea.
  • a method and apparatus are provided to generate tomography images that performs the method.
  • the apparatus and method are configured to determine a basis pattern from modulated phases of incident rays from a spatial light modulator according to a pattern of arranged pixels.
  • the apparatus and method are further configured to perform spatial shift modulation shifting an arrangement of the pixels vertically or horizontally with respect to the basis pattern to obtain shift patterns of the basis pattern.
  • the apparatus and method are configured to generate tomography images for the basis pattern and the shift patterns using spectrum signals of rays obtained from the incident rays passing through the spatial light modulator and entering a subject.
  • the apparatus and method are configured to select a pattern that generates a clearest tomography image of the subject based on the generated tomography images.
  • the American patent application US20160299060A1 discloses an immersion probe system for simultaneously performing first analysis of a first portion of light originating from liquids and/or particles in a fluid and second analysis of a second portion of the light originating from the liquids and/or particles.
  • the system defines an optical axis and includes a first component including a first analyzer, a window, and a first optical path extending between the window and the first analyzer.
  • the system also includes a second component including a second analyzer, the window, and a second optical path extending between the window and the second analyzer.
  • the system further includes a spectral selector placed in the first optical path and in the second optical path to direct the first portion of the light, which originates from the liquids and/or particles and passes through the window, to the first analyzer, and to direct the second portion of said light to the second analyzer.
  • the system includes an illumination path that delivers illumination light or lights based on a beam(s) that passes through the window at an oblique or normal angle to the optical axis.
  • the first component and the second component share a common optical path at least between the window and the spectral selector.
  • the invention relates to all OCT methods with parallel Fourier domain detection, which use a spatially coherent light source.
  • it can be used in systems with parallel detection in the plane (X,Y) in which each pixel of a one- or two-dimensional detector, sequentially in time, records spectral interference fringes generated during the change of the optical frequencies of a rapidly tunable laser (Swept Source).
  • Swept Source a rapidly tunable laser
  • It can also be used in systems with parallel detection in the plane (X,Z), where simultaneously a set of spectral interference fringes are recorded, which correspond to one line in the plane (X,Y) using an imaging spectrometer equipped with a two-dimensional photodetector array and a light source emitting spectral broadband radiation.
  • the aim of the invention is to improve the quality of the cross-sectional imaging using OCT with parallel Fourier domain detection, by a significant reduction of optical crosstalk.
  • the present invention also makes it possible to significantly reduce the contrast of speckle noise.
  • An improvement in the quality of imaging by filtering out unwanted light which, as randomly scattered on the structure of the examined object, opens up the possibilities of imaging other, deeper biological structures than in classical OCT, in particular the possibility of imaging of the choroidal layer.
  • the invention introduces a new imaging method including measurement and data analysis and a new apparatus as a measuring system using this method.
  • the invention achieves the above goal, i.e. the reduction of optical crosstalk through the unobvious use of tools typical of techniques for the optical selection of the imaging plane to OCT with parallel Fourier domain detection.
  • the unobvious combination of these techniques also implies an unobvious modification of the design of the apparatus for OCT with parallel Fourier domain detection.
  • the subject of the invention is an apparatus for imaging objects by OCT with parallel Fourier domain detection, comprising a light source, a multi-element photo-detector, an interferometer containing at least one beam splitter, a reference mirror, two optical systems and an optical system forming an image on a multi-element photodetector, characterized in that an instrument for spatially varying modulation of the phase of light and a device for independent control of the angular distribution of sample illumination are placed before beamsplitting means, configured to split the beam emitted by the light source into the reference beam and object beam
  • the apparatus for spatially varying modulation of the phase of light comprises an active element selected from the group including a rotating or sliding diffuser, a mirror comprising a two-dimensional array of piezoelectric or liquid crystal elements or a vibrating light reflecting membrane, preferably in the form of a deformable mirror.
  • the apparatus for changing the angles of illumination is: a DMD (Digital Micromirror Device) system, an acousto-optical deflector, a liquid crystal spatial light modulator, an electro-optical deflector, a MEMS (microelectromechanical system) or at least one resonance or galvanometric scanner equipped with at least one mirror mounted on at least one galvanometer engine.
  • the device that enables changing the angles of illumination can also be any other system deflecting the light beam.
  • the device may also be a liquid crystal spatial light modulator, which introduces into the cross-section of the beam a phase ramp in a different orientation and inclination resulting in changes in the angle of illumination of the sample.
  • the device introducing spatially varying modulation of the phase of light and the additional device to change the angles of illumination can be one device that performs both functionalities by simultaneously or sequentially applying the appropriate phase masks, for example phase ramps and random phase distributions. Also, changing the position of the light source in the plane Fourier-conjugated with the object plane can be used to change the angle of illumination of the sample.
  • the optical system forming light on the object and the optical system forming light on the reference mirror comprise the same optical elements.
  • the device introducing spatially varying modulation is configured to modulate light phase
  • the device for changing the illumination angles, configured to control the sample illumination angle are physically separated and configured to operate independently.
  • the detector is: a one-dimensional camera, a two-dimensional camera, a collection of photodiodes, or an imaging spectrometer that allows simultaneous recording of spectra for different points of the object.
  • the multi-element photodetector is a line of photosensitive elements
  • an imaging spectrometer wherein an additional cylindrical optics is between the light source and the instrument, and a beam scanning device is in the interferometer object arm between the beam splitter and the optical system, for example a galvanometric scanner configured to deflect the beam in one direction.
  • a beam scanning device for example a galvanometric scanner configured to deflect the beam in one direction.
  • the light source is a device allowing for a sweeping with optical frequencies or wavelengths with a spectral width greater than 0.5 nm. Then, when the detector is an imaging spectrometer the light source is a device allowing the generation of spatially coherent light with a spectrum with a spectral width greater than 0.5 nm.
  • the invention also relates to the method of OCT with parallel Fourier domain detection using a spectrally broadband light source, and multi-element photodetector used to create three-dimensional image reconstruction of the structure of the object, comprising steps of:
  • the phase values in the beam cross-section change randomly or according to a predetermined function.
  • complex averaging is performed by integration on a multi-element detector at a given exposure time.
  • complex averaging is performed by numerically adding the signals of complex representations of the interference images obtained from multiple measurements.
  • the image of the beam cross-section in which the spatial phase modulation takes place is formed in an object plane.
  • the spatial frequency spectrum corresponding to the cross section of the beam in which the spatial phase modulation takes place is formed in an object plane
  • successive interferometric images recorded sequentially over time by a multi-element detector correspond to different optical frequencies generated over time by a broadband light source.
  • the interferometric images are recorded in the form of a set of spectra recorded by a multi-element light detector.
  • the image reconstruction process is repeated for different illumination angles of the object and then the image reconstructions obtained for different illumination angles are averaged to obtain a final reconstruction of the three-dimensional image of the object.
  • the light beam illuminating the object is formed into a line and spatial phase modulation is along the direction defined by the light beam formed into the line.
  • the subject of the invention is also the method for OCT with parallel Fourier domain detection as described above, using a device for imaging objects by the technique described above.
  • OCT with parallel Fourier domain detection using a multi-element photodetector involves the recording of a plurality of interferometric images resulting from reflection or backscattering of the light from the object being examined and the reference mirror by means of a multi-element detector, where each of these images is measured when the phase of light entering the interferometer is modulated in the cross-section of the beam (spatially varying modulation of the phase of light).
  • This modulation can be performed repeatedly during the exposure time of the camera, or sequentially for subsequent recorded interferometric images, which are later averaged in a complex manner during the numerical processing of the signals.
  • the entire procedure is repeated several times for different angles of illumination of the sample introduced by a device changing the illumination angles.
  • various interferometric signals are generated, for example by controlled deflection of the light beam in front of the interferometer, so that the change in the illumination angle is the same for the light illuminating the reference mirror and the measured object.
  • the image reconstructions obtained in this manner are averaged giving the final form of image reconstruction free from the presence of undesirable effects i.e. optical crosstalk and speckle noise, which affect the imaging of three-dimensional objects, especially in-vivo imaging.
  • Various interferometric signals are generated by means of an element (device) introducing spatially varying modulation of the phase of light and can be carried out in two ways:
  • the phase mask used to modulate the phase of light which is employed by the device introducing spatial modulation of the phase of light may be a random phase distribution.
  • the size of the smallest fixed phase element in a given random mask should match the numerical aperture of the system so that the light scattered due to such phase modulation is not vignetted by the elements of the optical system.
  • An effect analogous to the elimination of optical crosstalk can be obtained by introducing deterministic phase masks used for phase modulation, given by a device introducing phase modulation, such as, for example, a time-variable array of Hadamard phase masks or Zernike polynomials.
  • the interferometer system can be designed in many ways, including typical interferometers such as the Michelson, Twyman-Green, Linnik or Mach-Zender interferometers.
  • the transmission object may be in one of the arms of the Mach-Zender interferometer.
  • a fiber-optic interferometric device is possible - but the fiber optic used here must be multimode or it must be a bundle of single-mode optical fibers.
  • the apparatus is the use of a light source emitting short femtosecond pulses or Amplified Spontaneous Emission light (ASE) with a spectral width greater than 0.5 nm.
  • the multi-element light detector may be an imaging spectrometer, i.e. a device that measures light spectra for successive points of a one-dimensional image of the sample.
  • the system forming the light field on the object together with the system forming the light field on the reference mirror form a beam of light in a line that illuminates the object and the reference mirror.
  • the linear images of the surface of the reference mirror and the object are mapped in one dimension in the system of the imaging spectrometer, while the second dimension enables the separation of the components of the optical wavelengths.
  • this is accomplished by using at least one cylindrical lens, a slit or a suitable diffractive element.
  • the image forming systems inside the interferometer can consist of identical optical elements creating the Linnik interferometer system.
  • the natural optical system of the eye becomes a component of the optical system forming light on the object whilst the optical system forming light on the reference mirror has optical elements mimicking the optical parameters of the eye's optical system in such a way that the optical system in the reference arm and the imaging system together with the human eye are equivalent.
  • OB - object DET - detector (photodetector); D1 - device (component) introducing phase modulation (for phase modulation), the so-called spatial light modulator; D2 - device (component) for changing the illumination angles; M1 - reference mirror; LS - light source; BS - beam splitter; L0-L12 achromatic biconvex lenses; OF - optical fiber, U0-U3 optical sets forming a beam; PC - computer; GM - galvanometric scanner, DM - deformable mirror; CL - collimator; CMOS - fast camera; L-CMOS - fast camera with a line of detectors (when the DET detector is in the form of a line of light-sensitive elements); P0-2 - light source image mapping points; 1D-GS - galvanometric scanner deflecting the beam in one direction; LC - cylindrical lens, IS - imaging spectrometer, DG - diffraction
  • the optical system depicted in Figure 3 was employed to carry out the measurement method , which is not part of the claimed invention, consisting of the recording of a plurality of interferometric images measured during the modulation of the spatial phase of light entering the interferometer system.
  • a key element of the presented method is the Dyoptyka DM phase-randomizing deformable mirror with a unique design. This mirror is a thin membrane that vibrates at a frequency of above 200 kHz. These vibrations are induced in conditions that are different to those for obtaining transverse resonance modes on the surface of the membrane. As shown in Fig.
  • the phase-randomizing deformable mirror DM which together with lenses L0 and L1 with 50mm focal length performs the function of the device D1 is placed in the path of the light beam, formed by the collimator CL, emitted from the light source LS through a single-mode optical fiber OF.
  • the light source LS is the Superlum Swept Source Broadsweeper rapidly tunable laser, which allows for rapid sweep of optical frequencies, in a band of about 70 nm with a central wavelength of 840 nm in the spatially generated coherent beam of light.
  • the spatially modulated beam is split by the beam splitter BS (Thorlabs BS014) and half of the energy is directed to the reference arm of the interferometer and the other half to the object arm.
  • the multi-element light detector DET which is a Photron FastCam CMOS fast camera.
  • the phase is spatially modulated by the membrane fluctuations in a time shorter than the exposure time of the CMOS camera - in this example the phase change takes place in less than 5 microseconds. Therefore, the interference image recorded by the CMOS camera for one optical frequency of the wave generated by the swept source LS is the result of the averaging of many interferometric signals. Since this averaging takes place during the opening of the CMOS camera shutter (complex averaging) the phase relations in the beams from the reference arm and the object arm of the interferometer are retained only for those waves that do not undergo strong distortions of the wavefront in one of the interferometer arms.
  • Distorted waves which are responsible for the crosstalk effect, interfere with variable phases, meaning that the visibility of the interferometric fringes from these waves is less than imaging noise.
  • new, crosstalk-free interference images are recorded by the CMOS camera for successive optical frequencies generated by the light source LS. Recording of interference images is repeated many times for different optical frequencies until a set of signals enabling the reconstruction of the three-dimensional structure of the object Ob in a manner typical of the OCT technique with parallel Fourier domain detection is obtained.
  • the measuring process involves the following example sequence of activities:
  • the signal processing required to reconstruct the structure of the tested object is identical to the method of analysis of data obtained by OCT with parallel Fourier domain detection, which is known from the literature.
  • Figure 4 shows the result of the above described measuring process, which is not part of the claimed invention, along with the result obtained by means of the device according to the scheme known from the state of the art ( Fig 1 ).
  • the measurement was carried out using a phantom consisting of two scattering layers immersed in a transparent material as the object Ob.
  • One scattering layer with a thickness of about 15 microns is above the second layer, the thickness of which is a few millimeters.
  • the logotype fragments In the pictures of cross-sections Fig.4.a1 and Fig.4.a2 the logotype fragments have the shape of rectangular blocks growing out of the scattering layers.
  • the use of derivative analysis of the spatial distribution of the intensity of the backward reflected signal from the sample allows a quantitative assessment of the improvement in the contrast of image reconstruction. In this case, a three-fold improvement in contrast was achieved, which made it possible to recognize the structure of the cavity surrounded by the light scattering material.
  • the use of the spatial modulator D1 enabled the elimination of the crosstalk effects manifested by a reduced contrast of the details of the components of the object located in the highly scattering layer (the spherical cavity).
  • the apparatus described in Example 1 is modified for human retinal imaging, as illustrated in Fig. 5 .
  • the optical systems U1 and U2 are adapted to the natural optics of the eye due to the fact that U1 has three achromatic lenses L4, L5 and L10 arranged in such a way that the plane of the entrance pupil of the imaging system coincides with the plane of the pupil of the human eye.
  • U2 has an additional lens L11 and in front of the reference mirror M1 there is another lens L12 with a focal length close to the focal length of the natural optical system of the eye.
  • the apparatus was used for retinal imaging and this was also achieved by abandonment of the L5, L10 and L7 and L11 lenses at the expense of less flexibility in the selection of enlargement on the retina.
  • Example 1 The apparatus described in Example 1 was used and the imaging method was OCT with parallel Fourier domain detection using this apparatus where the sample illumination is in the shape of a line and the light detector system DET is a one-dimensional L-CMOS camera, which is illustrated in Fig. 6 .
  • the deformable mirror DM In front of the deformable mirror DM, there is a cylindrical lens LC that forms a beam in the shape of a line on its surface.
  • three-dimensional reconstruction is achieved by placing an additional galvanometric scanner 1D-GS in front of the optical system U1, which allows for sweeping the line illuminating the object in a direction perpendicular to the direction determined by this line.
  • Fig. 7 shows a further modification of the apparatus in Example 1, in which instead of using a rapid tunable swept source laser, a spectral broadband light source LS emitting radiation containing a plurality of component optical frequencies is used.
  • this is a Femtolasers Fusion femtosecond laser fs-LS generating 6fs pulses with an output power of 300mW.
  • the modification of the optical system involves changing the detector from a line of photosensitive elements to an imaging spectrometer IS, including a camera with a 2-D CMOS array and an efficient Wasatch Photonics holographic diffraction grating DG (800 lines/mm).
  • an imaging spectrometer IS including a camera with a 2-D CMOS array and an efficient Wasatch Photonics holographic diffraction grating DG (800 lines/mm).
  • the light illuminating the sample is formed into a line by means of a cylindrical lens LC, and the three-dimensional reconstruction is achieved by placing an additional galvanometer scanner 1D-GS in front of the system U1, which allows for sweeping the object Ob with an illuminating line in a direction perpendicular to the direction designated by this line.
  • Example 1 The process of creating image reconstructions from Example 1 was repeated for different angles of illumination of the object Ob.
  • the modified apparatus shown in Example 1 was used for this, illustrated in Fig. 8 , in which there is additionally a device D2 for changing the illumination angles of the sample beam, which is a pair of Thorlabs galvanometric scanners GM additionally equipped with a mirror M.
  • a fast-response deformable mirror DM was used together with lenses L0 and L1 as the device D1 introducing phase modulation and a galvanometer scanner GM or 1D-GS together with lenses L2 and L3 as the device D2 to change the angle of incidence of the light illuminating the sample.
  • a Broadsweeper fast tunable laser TL was used as the light source.
  • the reference mirror M1 was installed on a translational stage that allows for precise positioning of the device.
  • the detector in this system is a fast CMOS camera.
  • the device D2 is placed after the laser LS and the device D1 comprising phase-randomizing deformable mirror DM. Light from the laser LS illuminates the deformable mirror DM, introducing spatially varying modulation of the phase of light. Further on, the beam falls on the mirror of the galvanometer scanner GM or 1D-GS.
  • the plane of the galvanometer scanner mirror GM or 1D-GS is optically conjugate to the plane corresponding to the surface of the deformable mirror DM.
  • the final image of the object and the reference mirror is formed by the optical system U3 comprising the above two lenses L8 and L9 arranged in the 4f configuration, on the detector DET.
  • Example 1 As in Example 1, as a result of this imaging, a set of interferometric signals is created on the CMOS camera which is specific to each of the wavelengths generated by the tunable light source LS for each phase modulation introduced by the deformable mirror DM. This time, however, the entire measurement containing a set of interferometric images obtained for various optical frequencies is repeated for several positions of the mirror of the galvanometric scanners GM in the instrument D2.
  • analysis of the effectiveness of reducing the contrast of speckle noise was carried out using a tissue phantom comprising two layers of highly scattering light material.
  • Figure 12.1 shows the result of the imaging method when only the instrument D2 is used to change the angles of illumination of the sample Ob.
  • CNR I S ⁇ ⁇ I N ⁇ ⁇ S 2 + ⁇ N 2
  • I S , I N are average signal and noise intensities
  • ⁇ S and ⁇ N are standard deviations of signal and noise.
  • CNR 1.37 for the data shown in Fig. 12.1 corresponding to the use of only the phase change device
  • D1 and CNR 2.1 for the data shown in Fig. 12.2 corresponding to the use of the devices D1 and D2.
  • FIG. 10 Another example of the apparatus and the method of OCT with parallel Fourier domain detection using the apparatus according to the invention is shown in Fig. 10 , which is a modification of the apparatus described in Example 5, the modification involves the illumination of the object Ob (the sample) in the shape of a line and the light detector system DET is a one-dimensional camera.
  • the galvanometer scanner GM operates in one dimension with the scan direction perpendicular to the direction determined by the scanner 1d-GS.
  • FIG. 11 A further embodiment of the apparatus and a method of imaging with OCT with parallel Fourier domain detection according to the invention is illustrated in Fig. 11 .
  • the apparatus is a modified system (apparatus) from Example 4 ( Fig. 7 ).
  • the apparatus works with the use of a spectral broadband LS light source emitting radiation containing many optical component frequencies.
  • a galvanometer scanner GM used as D2 operates in one dimension with the scanning direction perpendicular to the direction determined by the scanner 1d-GS.

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Claims (20)

  1. Vorrichtung zum Abbilden von Objekten mit Hilfe von OCT mit paralleler Fourierdomänendetektion, umfassend eine Lichtquelle (LS), einen mehrteiligen Fotodetektor (DET), ein Interferometer, das mindestens einen Strahlteiler (BS), einen Referenzspiegel (M1), zwei optische Systeme U1, U2 und ein auf dem Multielement-Fotodetektor (DET) ein Bild erzeugendes optisches System (U3), enthält, dadurch gekennzeichnet, dass eine Vorrichtung (D1) zur räumlich variierenden Modulation der Lichtphase im Strahlquerschnitt und eine Vorrichtung (D2) zur unabhängigen Steuerung der Winkelverteilung der Probenbeleuchtung vor dem mindestens einen Strahlteiler (BS) angeordnet sind, der so konfiguriert ist, um den von der Lichtquelle emittierten Strahl in einen Referenzstrahl und einen Objektstrahl aufzuteilen.
  2. Vorrichtung nach Anspruch 1, dadurch gekennzeichnet, dass die Vorrichtung (D1), die eine räumlich variierende Modulation der Lichtphase einführt, ein aktives Element umfasst, das aus der Gruppe ausgewählt ist, die einen rotierenden oder verschiebbaren Diffusor, einen eine zweidimensionale Anordnung von piezoelektrischen oder Flüssigkristallelementen enthaltenden Spiegel, oder eine das Licht reflektierende vibrierende Membran, vorzugsweise in Form eines deformierbaren Spiegels (DM), umfasst.
  3. Vorrichtung nach Anspruch 1, dadurch gekennzeichnet, dass die Vorrichtung (D2) zum Ändern der Beleuchtungswinkel eine digitale Mikrospiegeleinrichtung DMD, ein akustooptischer Deflektor, ein elektrooptischer Deflektor, ein Flüssigkristall-Raumlichtmodulator, ein elektromechanisches Spiegel-Mikrosystem (MEMS) oder mindestens ein resonanter oder galvanometrischer Scanner (GM), der mit mindestens einem, an mindestens einem Galvanometermotor montierten Spiegel ausgestattet ist, ist.
  4. Vorrichtung nach einem der vorangehenden Ansprüche 1 bis 2, dadurch gekennzeichnet, dass die zur Modulation der Lichtphase konfigurierte Vorrichtung (D1) und die zur Steuerung des Probenbeleuchtungswinkels konfigurierte Vorrichtung (D2) physikalisch getrennt und separat konfiguriert sind, um unabhängig voneinander zu arbeiten.
  5. Vorrichtung nach einem der vorhergehenden Ansprüche 1 bis 4, dadurch gekennzeichnet, dass das das Licht auf dem Objekt (Ob) bildende optische System U1 und das das Licht auf dem Referenzspiegel (M1) bildende optische System U2 ähnliche optische Elemente umfassen.
  6. Vorrichtung nach einem der vorangehenden Ansprüche 1 bis 5, dadurch gekennzeichnet, dass der mehrteilige Fotodetektor (DET) eine eindimensionale Kamera (LCMOS), eine zweidimensionale Kamera (CMOS), eine Fotodiodenanordnung oder ein bildgebendes Spektrometer (IS), das die gleichzeitige Aufnahme von Spektren ermöglicht, indem sie für verschiedene Punkte des Objekts (Ob) abgebildet werden, ist.
  7. Vorrichtung nach einem der vorangehenden Ansprüche 1 bis 6, dadurch gekennzeichnet, dass der mehrteilige Fotodetektor (DET) eine Zeile fotoempfindlicher Elemente (LCMOS) oder ein bildgebendes Spektrometer (IS) ist, wobei ein zusätzliches zylindrisches Optikelement zwischen der Lichtquelle (LS) und dem Vorrichtung (D1) vorkommt, und eine Strahlabtasteinrichtung im Objektarm des Interferometers zwischen dem mindestens einen Strahlteiler (BS) und dem optischen System U1 vorkommt, wobei eine Strahlabtasteinrichtung beispielsweise ein galvanometrischer Scanner, der so konfiguriert ist, dass er den Strahl in eine Richtung ablenkt (ID-GS), ist.
  8. Vorrichtung nach einem der vorangehenden Ansprüche 1 bis 7, dadurch gekennzeichnet, dass der mehrteilige Fotodetektor (DET) eine eindimensionale Kamera (LCMOS) oder eine zweidimensionale Kamera (CMOS) ist und die Lichtquelle (LS) eine Vorrichtung, die einen Sweep von optischen Frequenzen oder Wellenlängen mit einer eine spektrale Bandbreite von mehr als 0,5 nm abdeckende Sweep-Spanne ermöglicht.
  9. Vorrichtung nach Anspruch 7, dadurch gekennzeichnet, dass der mehrteilige Fotodetektor (DET) ein bildgebendes Spektrometer (IS) ist und die Lichtquelle (LS) eine Vorrichtung, die Erzeugung von räumlich kohärentem Licht (fs-LS) mit einem Spektrum ermöglicht, das sich über eine Bandbreite von mehr als 0,5 nm erstreckt, ist.
  10. Ein Bildgebungsverfahren unter Mithilfe von optischer Kohärenztomographie mit Parallel-Fourier-Domänen-Detektion unter Verwendung einer spektral breitbandigen Lichtquelle (LS) und eines mehrteiligen Fotodetektors (DET) zum Erstellen einer dreidimensionalen Bildrekonstruktion der Struktur des Objekts (Ob), umfassend die Schritte:
    a) Aufspalten des Lichts durch einen Strahlteiler (BS) in einen Referenz- und Objektstrahl,
    b) dynamische Modulation der Lichtphase räumlich und zeitlich durch Verwendung der Vorrichtung (D1) und der Vorrichtung (D2), die zwischen der Lichtquelle und dem Strahlteiler angeordnet sind, dadurch gekennzeichnet, dass die Vorrichtung (D1) für eine dynamische räumliche Lichtphasenmodulation über den Strahlquerschnitt sorgt und die Vorrichtung (D2) für eine unabhängige Steuerung der Winkelverteilung der Probenbeleuchtung sorgt, bevor der von der Lichtquelle (LS) emittierte Strahl durch den Strahlteiler (BS) in Referenz- und Objektstrahl aufgeteilt wird und die durch den mehrteiligen Fotodetektor (DET) erhaltenen Interferenzbilder aufwendig integriert werden.
  11. Verfahren nach Anspruch 10, dadurch gekennzeichnet, dass sich die Phasenwerte im Strahlquerschnitt zufällig oder nach einer vorgegebenen Funktion ändern.
  12. Verfahren nach Anspruch 10 oder 11, dadurch gekennzeichnet, dass eine komplexe Mittelwertbildung durch Integration auf einem mehrteiligen Fotodetektor (DET) bei gegebener Belichtungszeit durchgeführt wird.
  13. Verfahren nach einem der vorangehenden Ansprüche 10 bis 12, dadurch gekennzeichnet, dass eine komplexe Mittelwertbildung durch numerische Summierung von Signalen komplexer Darstellungen von Interferenzbildern durchgeführt wird, die aus mehreren Messungen erhalten wurden.
  14. Verfahren nach einem der vorhergehenden Ansprüche 10 bis 13, dadurch gekennzeichnet, dass das Bild des Strahlquerschnitts, in dem die räumliche Phasenmodulation erfolgt, in einer Objektebene gebildet wird.
  15. Verfahren nach einem der vorhergehenden Ansprüche 10 bis 14, dadurch gekennzeichnet, dass das Ortsfrequenzspektrum, das dem Strahlquerschnitt entspricht, in dem die Ortsphasenmodulation auftritt, in einer Objektebene gebildet wird.
  16. Verfahren nach einem der vorangehenden Ansprüche 10 bis 15, dadurch gekennzeichnet, dass die vom mehrteiligen Fotodetektor (DET) zeitlich sequentiell aufeinanderfolgend aufgenommenen interferometrischen Bilder den zeitlich unterschiedlichen der von der Breitbandlichtquelle (LS) generierten optischen Frequenzen entsprechen.
  17. Verfahren nach einem der vorhergehenden Ansprüche 10 bis 16, dadurch gekennzeichnet, dass die interferometrischen Bilder in Form eines Satzes der von einem mehrteiligen Fotodetektor (DET) aufgenommenen Spektren aufgezeichnet werden.
  18. Verfahren nach einem der vorhergehenden Ansprüche 10 bis 17, dadurch gekennzeichnet, dass der Vorgang der Bildrekonstruktion für unterschiedliche Beleuchtungswinkel des Objekts (Ob) wiederholt wird und anschließend die für unterschiedliche Beleuchtungswinkel erhaltenen Bildrekonstruktionen gemittelt werden, um eine endgültige Bildrekonstruktion der dreidimensionalen Struktur des Objekts (Ob) zu erhalten.
  19. Verfahren nach einem der vorhergehenden Ansprüche 10 bis 18, dadurch gekennzeichnet, dass der das Objekt (Ob) beleuchtende Lichtstrahl zu einer Linie geformt wird und die räumliche Phasenmodulation entlang der durch den in eine Linie geformten Lichtstrahl definierten Richtung durchgeführt wird.
  20. Abbildungsverfahren nach einem der vorhergehenden Ansprüche 10 bis 19, das in der Vorrichtung nach einem der vorhergehenden Ansprüche 1 bis 9 durchgeführt wird.
EP18461611.8A 2018-09-21 2018-09-21 Vorrichtung zur parallelen optischen kohärenztomographie-bildgebung im fourier-bereich und bildgebungsverfahren mit verwendung von paralleler optischer kohärenztomographie im fourier-bereich Active EP3627093B1 (de)

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PCT/IB2019/058008 WO2020058947A1 (en) 2018-09-21 2019-09-21 Apparatus for parallel fourier domain optical coherence tomography imaging and imaging method using parallel fourier domain optical coherence tomography

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